Organic light emitting element

ABSTRACT

Provided is an organic light emitting element having stable performance in the air. The organic light emitting element includes: an anode; a cathode; and an emission layer placed between the anode and the cathode, in which: the organic light emitting element further includes a first organic compound layer placed between the cathode and the emission layer, and a second organic compound layer placed between the emission layer and the first organic compound layer, and contacted with the first organic compound layer; the first organic compound layer contains a first organic compound; the second organic compound layer contains a second organic compound; and the first organic compound includes a viologen compound represented by the following general formula [1] and the second organic compound includes an organic compound different from the viologen compound.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an organic light emitting element, adisplay apparatus, an image information processing apparatus, a lightingapparatus, an image forming apparatus, and an exposing apparatus.

Description of the Related Art

An organic light emitting element (organic electroluminescence elementor organic EL element) is an electronic element including a pair ofelectrodes and an organic compound layer placed between the pair ofelectrodes. An electron and a hole are injected from the pair ofelectrodes, and then the electron and the hole recombine in the organiccompound layer to produce an exciton of a luminous organic compound. Theorganic light emitting element emits light upon return of the exciton toits ground state.

In the organic light emitting element, at least one organic compoundlayer is placed between the electrodes. As one layer constituting theorganic compound layer, there is known an electron injection layer thatserves to inject or transport an electron injected from a cathode intoan emission layer. For example, an alkali metal or alkaline earth metalderivative has been widely known as a constituent material for theelectron injection layer. It is because each of the alkali metal andalkaline earth metal derivatives is a material having a small workfunction and shows a good electron injection property that any suchderivative is used as the constituent material for the electroninjection layer. However, it has been known that each of the alkalimetal and alkaline earth metal derivatives is a material that easilyreacts with water. Accordingly, an organic light emitting elementcontaining any one of the alkali metal and alkaline earth metalderivatives as a constituent material for its electron injection layeris affected by moisture in the air. Therefore, at present, the organiclight emitting element needs to be stringently sealed so that theorganic light emitting element may not be exposed to the moisture in theair. Meanwhile, in order that the effect due to the moisture in the airmay be overcome, various researches and developments have been conductedon a method of stably driving the organic light emitting element even inthe air except the sealing.

As one method of improving the stability of the organic light emittingelement against the moisture in the air, for example, there is known amethod involving introducing Compound a-1 having an electron donorproperty and Compound a-2 having an electron acceptor property shownbelow into the electron injection layer like U.S. Patent ApplicationPublication No. 2005/0110005.

In the electron injection layer of the organic light emitting element ofU.S. Patent Application Publication NO. 2005/0110005, the compoundhaving an electron donor property (D molecule) donates an electron tothe compound having an electron acceptor property (A molecule), wherebycharge (an electron) is generated. In addition, a strong interactionoccurs between the D molecule and the A molecule to produce a polarizedDA complex. Thus, the organic light emitting element of U.S. PatentApplication Publication NO. 2005/0110005 can perform the injection of anelectron.

J. Org. Chem. 2008, 73, 445-450 discloses Viologen Compound b-1 shownbelow as a compound having a high electron donor property.

However, the HOMO of Compound a-1 (compound having an electron donorproperty) is deep and hence the energy level of the DA complex to beformed in the organic light emitting element of U.S. Patent ApplicationPublication No. 2005/0110005 is deep. Therefore, when Compounds a-1 anda-2 are used as constituent materials for the electron injection layerconstituting the organic light emitting element, an electron can beaccepted from an electrode (cathode) but a problem occurs in that abarrier for the injection of an electron into an emission layer is largeand hence good light emission is not obtained. Meanwhile, ViologenCompound b-1 disclosed in J. Org. Chem. 2008, 73, 445-450 has a highelectron donor property but its availability as a constituent materialfor an organic light emitting element has not been suggested. Inaddition, Viologen Compound b-1 itself has a large molecular weight andhence it has been difficult to subject the compound to sublimationpurification.

SUMMARY OF THE INVENTION

The present invention has been accomplished to solve the above-mentionedproblems and the present invention is directed to providing an organiclight emitting element having stable performance in the air.

An organic light emitting element according to a first aspect of thepresent invention includes: an anode; a cathode; and an emission layerplaced between the anode and the cathode, in which: the organic lightemitting element further includes a first organic compound layer placedbetween the cathode and the emission layer, and a second organiccompound layer placed between the emission layer and the first organiccompound layer, and contacted with the first organic compound layer; thefirst organic compound layer contains a first organic compound; thesecond organic compound layer contains a second organic compound; andthe first organic compound includes a viologen compound represented bythe following general formula [1] and the second organic compoundincludes an organic compound different from the viologen compound.

In the formula [1], R₁ to R₆ each represent a hydrogen atom or asubstituent selected from the group consisting of a fluorine atom, analkyl group, an alkoxy group, an aryl group, and a heteroaryl group,when any one of R₁ to R₆ represents an alkyl group or an alkoxy group,the alkyl group or the alkoxy group may further have a fluorine atom,and when any one of R₁ to R₆ represents an aryl group or a heteroarylgroup, the aryl group or the heteroaryl group may further have afluorine atom, an alkyl group, an alkoxy group, or an amino group.

An organic light emitting element according to a second aspect of thepresent invention includes: an anode; a cathode; and an emission layerplaced between the anode and the cathode, in which: the organic lightemitting element further includes an organic compound layer placedbetween the cathode and the emission layer; the organic compound layercontains a first organic compound and a second organic compound; and thefirst organic compound includes a viologen compound represented by thefollowing general formula [1] and the second organic compound includesan organic compound different from the viologen compound.

In the formula [1], R₁ to R₆ each represent a hydrogen atom or asubstituent selected from the group consisting of a fluorine atom, analkyl group, an alkoxy group, an aryl group, and a heteroaryl group,when any one of R₁ to R₆ represents an alkyl group or an alkoxy group,the alkyl group or the alkoxy group may further have a fluorine atom,and when any one of R₁ to R₆ represents an aryl group or a heteroarylgroup, the aryl group or the heteroaryl group may further have afluorine atom, an alkyl group, an alkoxy group, or an amino group.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating an example of adisplay apparatus including an organic light emitting element of thepresent invention and an active element connected to the organic lightemitting element.

FIG. 2 is a schematic view illustrating an example of an image formingapparatus including the organic light emitting element according to thepresent invention.

FIGS. 3A and 3B are each a schematic plan view illustrating a specificexample of an exposure light source constituting the image formingapparatus of FIG. 2.

FIG. 3C is a schematic view illustrating a specific example of aphotosensitive member constituting the image forming apparatus of FIG.2.

FIG. 4 is a schematic view illustrating an example of a lightingapparatus having the organic light emitting element according to thepresent invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

The present invention relates to an organic light emitting elementincluding an anode, a cathode, and an emission layer placed between theanode and the cathode. The organic light emitting element of the presentinvention including a first organic compound layer and second organiccompound layer described in the following (A), or an organic compoundlayer described in the following (B).

(A) A first organic compound layer placed between the cathode and theemission layer, and a second organic compound layer placed between theemission layer and the first organic compound layer, and contacted withthe first organic compound layer

(B) An organic compound layer placed between the cathode and theemission layer

When the organic light emitting element of the present inventionincludes the two layers (the first organic compound layer and the secondorganic compound layer) described in the (A), the first organic compoundlayer contains a first organic compound and the second organic compoundlayer contains a second organic compound. In the present invention, thefirst organic compound is a viologen compound represented by thefollowing general formula [1]. Meanwhile, in the present invention, thesecond organic compound is an organic compound different from theviologen compound represented by the following general formula [1].

It is to be noted that details about the viologen compound representedby the general formula [1] and the second organic compound are describedlater. In addition, when the organic light emitting element of thepresent invention includes the two layers (the first organic compoundlayer and the second organic compound layer) described in the (A), thefirst organic compound layer is preferably a layer contacted with thecathode.

Further, when the organic light emitting element of the presentinvention includes the organic compound layer described in the (B), theorganic compound layer contains a first organic compound and a secondorganic compound. In the present invention, the first organic compoundis a viologen compound represented by the general formula [1].Meanwhile, the second organic compound is an organic compound differentfrom the viologen compound represented by the general formula [1]. Whenthe organic light emitting element of the present invention includes theorganic compound layer described in the (B) as just described, theorganic compound layer is preferably a layer contacted with the cathode.

[Organic Light Emitting Element]

Hereinafter, a specific construction of the organic light emittingelement of the present invention is described.

In the organic light emitting element of the present invention, at leastthe emission layer is placed between the anode and the cathode as a pairof electrodes. In the present invention, the emission layer and anelectron injection layer as a layer closest to the cathode arepreferably placed between the anode and the cathode. However, in thepresent invention, layers to be placed between the anode and the cathodeare not limited to the emission layer and the electron injection layer.In addition to the emission layer and the electron injection layer, alayer such as a hole injection layer, a hole transport layer, a holeblocking layer, an electron transport layer, or an exciton blockinglayer may be appropriately introduced.

In addition, in the present invention, for example, an insulating layer,an adhesion layer, or an interference layer may be formed at aninterface between an electrode and a layer formed between the electrodes(such as the emission layer). Further, when a charge transport layer (anelectron transport layer or a hole transport layer) is incorporated as alayer to be formed between the electrodes, the charge transport layermay be constituted of a plurality of layers having different ionizationpotentials. As described above, the organic light emitting element ofthe present invention can adopt various layer constructions.

In the present invention, the light extraction construction of theorganic light emitting element may be a top emission system in whichlight is extracted from an electrode on a substrate side, or may be abottom emission system in which light is extracted from a side oppositeto the substrate. A construction in which light is extracted from eachof both the side closer to the substrate and the sides is alsopermitted.

[Viologen Compound (First Organic Compound, Electron Donor-PropertyCompound X)]

Next, the viologen compound represented by the following general formula[1] (first organic compound) as one constituent material for the organiclight emitting element of the present invention is described. It is tobe noted that the viologen compound represented by the general formula[1] is a compound having an electron donor property, and is preferablyused as a constituent material for a layer between the cathode and theemission layer. The compound is more preferably used as a constituentmaterial for a layer contacted with the cathode and is particularlypreferably used as a constituent material for the electron injectionlayer. In addition, in the following description, the viologen compoundrepresented by the general formula [1] is sometimes referred to as“electron donor-property compound X.”

In the general formula [1], R₁ to R₆ each represent a hydrogen atom or asubstituent selected from the group consisting of a fluorine atom, analkyl group, an alkoxy group, an aryl group, and a heteroaryl group.

Examples of the alkyl group represented by any one of R₁ to R₆ include amethyl group, an ethyl group, a n-propyl group, an isopropyl group, an-butyl group, a tert-butyl group, a n-hexyl group, a n-heptyl group,and a n-octyl group.

The alkyl group represented by any one of R₁ to R₆ is preferably analkyl group having 1 to 12 carbon atoms. This is because of thefollowing reason: as the number of carbon atoms of the alkyl groupincreases, the molecular weight of the entirety of the compoundincreases by an amount corresponding to the increase, which makes itdifficult to subject the compound to sublimation purification. However,the alkyl group has an effect of forming a good amorphous film. Inaddition, the alkyl group is a substituent having an electron-donatingeffect and hence the introduction of the group into the electrondonor-property compound X represented by the general formula [1] canadditionally reduce the oxidation potential of the compound itself.

An example of the alkoxy group represented by any one of R₁ to R₆ is amethoxy group.

The alkoxy group represented by any one of R₁ to R₆ is preferably analkoxy group having 1 to 12 carbon atoms. This is because of the samereason as that of the alkyl group. In addition, the alkoxy group is asubstituent having an electron-donating effect larger than that of thealkyl group and hence the introduction of the group into the electrondonor-property compound represented by the general formula [1] canadditionally reduce the oxidation potential of the compound itself.

It is to be noted that when any one of R₁ to R₆ represents an alkylgroup or an alkoxy group, the alkyl group or the alkoxy group mayfurther have a fluorine atom. That is, at least part of hydrogen atomsin the alkyl group or the alkoxy group may be substituted with afluorine atom. The alkyl group or alkoxy group as a substituent at leastpart of the hydrogen atoms of which are substituted with fluorine asdescribed above exhibits the following effect: by virtue of thehydrophobic effect or oleophobic effect of a fluorine atom, the compounditself has additional difficulty in reacting with moisture or oxygen inthe air and is improved in sublimation property.

Examples of the aryl group represented by any one of R₁ to R₆ include aphenyl group, a biphenyl group, a terphenyl group, a naphthyl group, aphenanthryl group, and a fluorenyl group.

The aryl group represented by any one of R₁ to R₆ is preferably an arylgroup having 6 to 18 carbon atoms. This is because as the molecularweight increases, it becomes more difficult to perform sublimationpurification. Examples of the aryl group having 6 to 18 carbon atomsinclude a phenyl group, a biphenyl group, a terphenyl group, a naphthylgroup, a phenanthryl group, and a fluorenyl group.

Examples of the heteroaryl group represented by any one of R₁ to R₆include a pyridyl group, a biphenylpyridyl group, a pyrimidyl group, atriazinyl group, a thienyl group, a furyl group, a pyrrolyl group, animidazolyl group, a benzimidazolyl group, a triazolyl group, abenzothienyl group, a dibenzothienyl group, a quinolyl group, and asubstituent shown below.

In addition, when any one of R₁ to R₆ represents an aryl group or aheteroaryl group, the aryl group or the heteroaryl group may furtherhave a fluorine atom, an alkyl group such as a methyl group, an ethylgroup, an isopropyl group, or a tert-butyl group, an alkoxy group suchas a methoxy group, or an amino group.

By the way, when a substituent represented by any one of R₁ to R₆ of theviologen compound represented by the general formula [1] isappropriately changed, any one of the physical properties of thecompound itself, specifically its oxidation potential, film property,heat stability, and sublimation property can be finely adjusted. Here,while the introduction of an electron-donating substituent reduces theoxidation potential, the introduction of an electron-withdrawingsubstituent increases the oxidation potential. It is to be noted thatout of the substituents (R₁ to R₆) in the formula [1], R₁ and R₂ largelycontribute to a change in the oxidation potential.

In the present invention, the viologen compound represented by thegeneral formula [1] (electron donor-property compound X) can be usedalone as a constituent material for the electron injection layer of theorganic light emitting element. This is because the stack of anextremely thin layer of the compound on an electrode (a metal electrodeor the cathode) reduces the work function of the electrode. However, inthe present invention, in addition to the electron donor-propertycompound X, a compound different from the electron donor-propertycompound X may be introduced into the electron injection layer. Inaddition, in the present invention, a layer containing the compounddifferent from the electron donor-property compound X may be formed soas to be brought into contact with the electron injection layer. Thecompound different from the electron donor-property compound X as usedherein is preferably an electron acceptor-property compound Y to bedescribed below.

[Electron Acceptor-property Compound Y (Second Organic Compound)]

Next, the second organic compound as one constituent material for theorganic light emitting element of the present invention is described. Inthe present invention, the second organic compound is preferably theelectron acceptor-property compound Y as a constituent material for theelectron injection layer. In the present invention, the electronacceptor-property compound Y is a compound having the followingfunction: the compound accepts an electron from the electrondonor-property compound X and emits the accepted electron toward anyother organic compound layer such as the emission layer. In the presentinvention, the electron acceptor-property compound Y is preferablyrepresented by any one of the following general formulae [2-1] to[2-21], [3-1], and [3-2].

In the formulae [2-1] to [2-21], [3-1], and [3-2], R₂₁ to R₉₉ and R₁₀₃to R₁₅₉ each represent a hydrogen atom or a substituent selected fromthe group consisting of an alkyl group, an alkoxy group, an aryl group,a heteroaryl group, and a fluorine atom.

Examples of the alkyl group represented by any one of R₂₁ to R₉₉ andR₁₀₃ to R₁₅₉ include, but of course not limited to, a methyl group, anethyl group, a n-propyl group, an isopropyl group, a n-butyl group, atert-butyl group, a n-hexyl group, a n-heptyl group, and a n-octylgroup. The alkyl group represented by any one of R₂₁ to R₉₉ and R₁₀₃ toR₁₅₉ is preferably an alkyl group having 1 to 12 carbon atoms.

An example of the alkoxy group represented by any one of R₂₁ to R₉₉ andR₁₀₃ to R₁₅₉ is a methoxy group.

Examples of the aryl group represented by any one of R₂₁ to R₉₉ and R₁₀₃to R₁₅₉ include, but of course not limited to, a phenyl group, abiphenyl group, a terphenyl group, a naphthyl group, an anthracenylgroup, a fluorenyl group, a phenanthryl group, a benzophenanthryl group,a chrysenyl group, a fluoranthenyl group, and a benzofluoranthenylgroup.

Examples of the heteroaryl group represented by any one of R₂₁ to R₉₉and R₁₀₃ to R₁₅₉ include, but of course not limited to, a pyridinylgroup, a pyrimidinyl group, a triazinyl group, a thienyl group, a furylgroup, a pyrrolyl group, an imidazolyl group, and a triazolyl group.

It is to be noted that when any one of R₂₁ to R₉₉ and R₁₀₃ to R₁₅₉represents an aryl group or a heteroaryl group, the aryl group or theheteroaryl group may further have an alkyl group such as a methyl group,an ethyl group, an isopropyl group, or a tert-butyl group, an alkoxygroup such as a methoxy group, an aryl group such as a phenyl group, aheteroaryl group such as a pyridyl group, or a fluorine atom.

In the formula [3-1], a unit Q represents a basic structure representedby any one of the formulae [2-1] to [2-21] or a partial structureincluding an aromatic ring having 6 to 30 carbon atoms. The partialstructure including an aromatic ring having 6 to 30 carbon atomscorresponding to the unit Q is, for example, a partial structure definedby any one of the following (A) to (C). However, in the presentinvention, the partial structure is not limited to the following.

(A) A complex substituent obtained by combining a basic structurerepresented by any one of the formulae [2-1] to [2-21] and an aryl group

(B) A complex substituent obtained by combining a plurality of arylgroups

(C) A condensed polycyclic substituent in which 6 or more carbon atomseach having an sp² hybrid orbital are present (A complex substituentformed of a plurality of partial structures is also included.)

Specific examples of the partial structure corresponding to the unit Qinclude the following partial structures. However, in the presentinvention, the partial structure is not limited to the following. It isto be noted that in the formulae, * represents an atomic bonding with aunit P to be described later.

In the formula [3-1], m represents an integer of from 0 to 6.

In the formula [3-1], the unit P represents any one of the followingsubstituents.

(In the formulae, R₁₀₀ and R₁₀₁ each represent a substituent selectedfrom the group consisting of a hydrogen atom, an alkyl group, an alkoxygroup, an aryl group, a heteroaryl group, and a fluorine atom. It is tobe noted that when any one of R₁₀₀ and R₁₀₁ represents an aryl group ora heteroaryl group, the aryl group or the heteroaryl group may furtherhave an alkyl group, an alkoxy group, an aryl group, a heteroaryl group,or a fluorine atom. * represents an atomic bonding with the unit Q. Itis to be noted that specific examples of R₁₀₀ and R₁₀₁ are the same asthose of R₂₁ to R₉₉ and R₁₀₃ to R₁₅₉.)

In the formula [3-2], a unit T represents a partial structure includingan aromatic ring having 6 to 30 carbon atoms or a partial structureincluding a five- or six-membered heterocyclic structure formed of acarbon atom and an oxygen atom.

The partial structure including an aromatic ring having 6 to 30 carbonatoms corresponding to the unit T is, for example, a partial structuredefined by the following (A) or (B). However, in the present invention,the partial structure is not limited to the following.

(A) A complex substituent obtained by combining a plurality of arylgroups

(B) A condensed polycyclic substituent in which 6 or more carbon atomseach having an sp² hybrid orbital are present (A complex substituentformed of a plurality of partial structures is also included.)

Specific examples of the partial structure corresponding to the unit Tinclude the following partial structures. However, in the presentinvention, the partial structure is not limited to the following. It isto be noted that in the formulae, * represents an atomic bonding with aunit Z to be described later.

In the formula [3-2], n represents an integer of from 0 to 6.

In the formula [3-2], the unit Z represents any one of the followingsubstituents.

(In the formulae, R₁₀₂ represents a substituent selected from the groupconsisting of a hydrogen atom, an alkyl group, an alkoxy group, an arylgroup, a heteroaryl group, and a fluorine atom. It is to be noted thatwhen R₁₀₂ represents an aryl group or a heteroaryl group, the aryl groupor the heteroaryl group may further have an alkyl group, an alkoxygroup, an aryl group, a heteroaryl group, or a fluorine atom. *represents an atomic bonding with the unit T. It is to be noted thatspecific examples of R₁₀₂ are the same as those of R₂₁ to R₉₉ and R₁₀₃to R₁₅₉.)

A compound represented by any one of the general formulae [2-1] to[2-21] is an electron-deficient condensed ring compound. Theelectron-deficient condensed ring compound preferably functions as anelectron acceptor because a n-electron of a condensed ring serving as abasic skeleton is deficient with respect to a benzene ring. Examples ofthe electron-deficient condensed ring compound include a pyridinecompound (formula [2-1]), a pyrimidine compound (formula [2-2]), atriazine compound (formula [2-3]), a quinoline compound (formula [2-4]),a naphthyridine compound (formula [2-6]), a phenanthroline compound(formula [2-7]), a fluoranthene compound (formula [2-8]), oxazolecompounds (formulae [2-10] and [2-17]), triazole compounds (formulae[2-11] and [2-18]), imidazole compounds (formulae [2-12] and [2-19]), anoxadiazole compound (formula [2-13]), a thiadiazole compound (formula[2-14]), and a triazole compound (formula [2-15]). However, theelectron-deficient condensed ring compound is not limited to thosecompounds and a compound formed by condensing a benzene ring or the liketo any one of those compounds (the formula [2-5], [2-9], [2-16], [2-20],or [2-21]) can also be used as the electron-deficient condensed ringcompound. Of course, the compound is not limited to the foregoing and acompound to be used in an electron transport layer is also permitted.

Each of the compounds represented by the general formulae [3-1] and[3-2] is a compound having an electron-withdrawing substituent. Here,the electron-withdrawing substituent increases the dipole moment of theentire molecule of the compound because the electron-withdrawing forceof the substituent itself causes polarization in the molecule.Accordingly, the compound preferably functions as an electron acceptor.Examples of the electron-withdrawing substituent include, but notlimited to, a substituent corresponding to the unit P (a nitro group, acyano group, a fluorine atom, a boron fluoride group, a phosphonylgroup, or a monovalent fluorinated alkyl group), and a substituentcorresponding to the unit Z (such as a carbonyl group, a sulfonyl group,an anhydride group, an imide group, a boron fluoride group, or a di- orhigher valent fluorinated alkyl group).

In the present invention, when an organic compound layer containing theviologen compound (electron donor-property compound) and the secondorganic compound (electron acceptor-property compound) is formed betweenthe cathode and the emission layer, a mixing ratio between both thecompounds in the organic compound layer is preferably adjusted in anappropriate manner. Specifically, the content of the second organiccompound (electron acceptor-property compound) in the organic compoundlayer is preferably more than 0 wt % and 80 wt % or less with respect tothe total of the viologen compound (electron donor-property compound)and the second organic compound.

[Relationship Between Electron Donor-Property Compound and ElectronAcceptor-Property Compound]

In the present invention, the effect of the present invention isexhibited by incorporating the electron donor-property compound and theelectron acceptor-property compound into the electron injection layerconstituting the organic light emitting element. It is to be noted thatthe electron injection layer may be of a stacked structure formed of theelectron donor-property compound X and the electron acceptor-propertycompound Y, or may be a mixed layer formed of the electrondonor-property compound X and the electron acceptor-property compound Y.In addition, in the present invention, the electron donor-propertycompound X and the electron acceptor-property compound Y preferablysatisfy the formula [4].|V _(red) −V _(ox)|1.0 V  [4]

In the formula [4], V_(red) represents the first reduction potentialvalue of the electron acceptor-property compound Y and V_(ox) representsthe first oxidation potential value of the electron donor-propertycompound X. It is to be noted that the V_(red) and the V_(ox) areoxidation-reduction potentials obtained by cyclic voltammetry (CV) underthe same measurement conditions. Here, the term “the same measurementconditions” means that a solvent, an electrolyte, a working electrode, areference electrode, a counter electrode, a temperature, and aconcentration are kept unchanged. In addition, in the measurement andevaluation of the oxidation-reduction potentials, the half-wavepotential value (E_(1/2)) of an oxidation-reduction wave that has beengenerally used is used.

Further, in the present invention, the electron donor-property compoundX and the electron acceptor-property compound Y preferably satisfy theformula [5].|V _(red) −V _(ox)|≦0.5 V  [5]

The electron injection layer constituting the organic light emittingelement of the present invention contains the electron donor-propertycompound X (viologen compound) and the electron acceptor-propertycompound Y, and hence the following significant effect is obtained: theelement is stably driven even in the air.

By the way, the electron injection layer constituting the organic lightemitting element is required to have at least characteristics (i) and(iii) out of the three characteristics listed below.

(i) An ability to accept an electron from the cathode (or an ability todonate a hole to the cathode)

(ii) An ability to transport charge (an electron) (in the layer)

(iii) An ability to inject an electron into an organic compound layerpositioned on a side opposite to the cathode (such as an electrontransport layer, a hole blocking layer, or the emission layer)

Unless the layer has at least the characteristics (i) and (iii) out ofthe characteristics (i) to (iii), an electron injected from the cathodecannot be injected into the emission layer and hence good light emissionfrom the emission layer is not obtained. It is to be noted that anelectron injection layer using an alkali metal or an alkaline earthmetal, or a derivative thereof as its constituent material has all thecharacteristics (i) to (iii) but is not preferred because the electroninjection layer easily reacts with a component in the air, especiallywater to result in its alteration.

The organic light emitting element disclosed in U.S. Patent ApplicationPublication No. 2005/0110005 also contains an electron donor-propertycompound and an electron acceptor-property compound in its electroninjection layer but does not provide good light emission. The reason forthe foregoing is described below.

In general, there is a large energy barrier between a cathode and anorganic compound layer (such as an electron transport layer, a holeblocking layer, or an emission layer). The HOMO of the electrondonor-property compound (Compound a-1) disclosed in U.S. PatentApplication Publication No. 2005/0110005 and the LUMO of the electronacceptor-property compound (Compound a-2) disclosed therein are each−4.5 eV, which is substantially equal to the work function (4.3 eV) ofaluminum that has been generally used as a cathode. Therefore, an energybarrier with respect to, for example, the LUMO (−3.3 eV) of Alq₃ thathas been normally used as a light emitting material in an organic lightemitting element enlarges. Accordingly, even when the DA complexdescribed in U.S. Patent Application Publication No. 2005/0110005 isintroduced into a layer (an electron transport layer or an electroninjection layer) having an electron injection/transport propertyconstituting an organic light emitting element, a voltage needed fordriving the element increases, and as a result, good light emission fromits emission layer is not obtained.

In contrast, the electron donor-property compound (viologen compound) tobe used as a constituent material for the electron injection layer inthe organic light emitting element of the present invention has thefollowing advantages: the compound has a high electron donor property,has a low first oxidation potential, and has a shallow HOMO (in adirection approaching a vacuum level).

Here, the following compounds are considered from the viewpoint of anoxidation-reduction potential on the assumption that there is acorrelation between a first oxidation potential and a HOMO, and there isalso a correlation between a first reduction potential and a LUMO.

The compounds were subjected to CV measurement under the sameconditions. As a result, the first oxidation potentials of Compound a-1and Compound B1 were 0.3 V and −1.2 V, respectively. The foregoing showsthat Compound B1 has a higher electron donor property because the firstoxidation potential of Compound B1 is smaller than that of Compound a-1by 1.5 V. Therefore, when the viologen compound represented by thegeneral formula [1] is adopted as an electron donor-property compound toestablish a state where a DA complex is formed in the electron injectionlayer, the ability to inject an electron into the organic compound layer(such as the electron transport layer, the hole blocking layer, or theemission layer) increases. As a result, good light emission from theemission layer is obtained.

In the organic light emitting element of the present invention, theelectron injection layer includes: a mixed film formed of the electrondonor-property compound X (viologen compound) and the electronacceptor-property compound Y; and a stacked film obtained by stackingthe electron donor-property compound X (viologen compound) and theelectron acceptor-property compound Y. Accordingly, in any case, thetransfer of charge from the electron donor-property compound X to theelectron acceptor-property compound Y or the production of a DA complexpolarized by a strong interaction between both the compounds occurs.Here, such interaction occurs between the HOMO of the electrondonor-property compound X and the LUMO of the electron acceptor-propertycompound Y. In addition, in the case where the electron injection layeris of a stacked structure, charge occurs between the electronacceptor-property compound and the electron donor-property compound, andhence an electron is easily accepted from the electrode (cathode). Onthe other hand, in the case of a mixed layer, the DA complex has acarrier and hence the charge mobility of the layer itself increases.Therefore, the electron injection layer constituting the organic lightemitting element of the present invention is excellent in electrontransport ability as well as in electron injection ability.

In addition, with regard to the relationship of the DA complex, it hasbeen generally known that as the oxidation potential of the electrondonor-property compound X and the reduction potential of the electronacceptor-property compound Y become closer to each other, a strongerinteraction occurs between the D and A molecules.

Therefore, specifically, as represented by the general formula [4], thepotential difference (|V_(red)−V_(ox)|) obtained by CV measurement ispreferably within 1.0 V. The potential difference is more preferablywithin 0.5 V as represented by the general formula [5]. This is becauseadditionally reducing the potential difference additionally strengthensthe interaction between the D and A molecules.

Compound b-1 shown below, which is disclosed in J. Org. Chem. 2008, 73,445-450, is a viologen compound having a high electron donor property.

However, Compound b-1 has a large molecular weight and hence it isdifficult to subject the compound to sublimation purification. Noexamples of the application of Compound b-1 to an electronic device suchas an organic light emitting element have been shown probably because ofthe foregoing. In general, a compound to be used as a constituentmaterial for an organic light emitting element needs to have a highpurity in order that the durability of the element may be improved.Therefore, whether a compound of interest can be subjected tosublimation purification as (one of) the methods of increasing thepurity of the compound itself is important.

In this respect, the electron donor-property compound X represented bythe general formula [1] (viologen compound) has a molecular weightsmaller than that of Compound b-1 and hence can be subjected tosublimation purification.

By the way, an organic compound having a high electron donor propertyand a small first oxidation potential generally tends to be readilyoxidized in the air. However, the viologen compound to be used as theelectron donor-property compound X is a compound that stably existswithout being quickly oxidized even in the air. Therefore, the organiclight emitting element of the present invention is stable even against afactor involved in the degradation of the organic light emitting elementsuch as oxygen in the air despite the fact that the element contains thecompound having a high electron donor property.

As described above, the electron injection layer constituting theorganic light emitting element of the present invention cansatisfactorily perform the injection of an electron from the cathode,the transport of an electron, and the injection of an electron into anorganic compound layer (such as the electron transport layer, the holeblocking layer, or the emission layer). In addition, an organic lightemitting element that is stable in the air can be provided by:introducing the electron donor-property compound X represented by thegeneral formula [1] (viologen compound) and the electronacceptor-property compound Y into the electron injection layer; andsatisfying the formula [4] between the compound X and the compound Y.

[Specific Examples of Electron Donor-Property Compound X]

Specific examples of the electron donor-property compound X (viologencompound) to be used as a constituent material for the organic lightemitting element of the present invention are shown below. However, thepresent invention is not limited to these specific examples.

[Properties of Exemplified Compounds (Electron Donor-Property CompoundX)]

Hereinafter, the compounds listed as the specific examples of theelectron donor-property compound X are described.

By the way, any one of the physical properties of the electrondonor-property compound X itself, specifically its oxidation potential,film property, heat stability, and sublimation property can be finelyadjusted depending on the kinds and number of substituents to beintroduced into a viologen skeleton as the basic skeleton of thecompound. Those physical properties can be appropriately selecteddepending on use purposes.

Each of the exemplified compounds is a compound having a high electrondonor property because all the compounds have viologen basic skeletons.Accordingly, a compound that improves stability against the air ispreferred. In the present invention, in particular, the following twokinds of compounds are given as a group of compounds that improvestability against the air. It is to be noted that the compoundrepresented by the following general formula [6] includes compoundsbelonging to the C group or the D group out of the listed exemplifiedcompounds, and the compound represented by the following general formula[7] includes the compounds belonging to the B group out of the listedexemplified compounds.

In the general formula [6], Ar₁ and Ar₂ each represent an aryl group.

Examples of the aryl group represented by Ar₁ or Ar₂ include a phenylgroup, a biphenyl group, a terphenyl group, a naphthyl group, ananthracenyl group, a fluorenyl group, a phenanthryl group, abenzophenanthryl group, a chrysenyl group, and a fluoranthenyl group.

In addition, the aryl group may further have a fluorine atom, an alkylgroup such as a methyl group, an ethyl group, an isopropyl group, or atert-butyl group, an alkoxy group such as a methoxy group, or an aminogroup.

The compound represented by the general formula [6] is preferred becauseof the following reason: the planarity of its viologen main skeleton isimproved and the intermolecular stacking property of the compound isimproved by substituting the main skeleton with an aryl group having ahigh stacking effect as a substituent, and hence the penetration of theair can be suppressed.

In the general formula [7], R₂₀₁ to R₂₀₆ each represent a substituentselected from the group consisting of a fluorine atom, an alkyl group,an alkoxy group, and an aryl group.

Examples of the alkyl group represented by any one of R₂₀₁ to R₂₀₆include a methyl group, an ethyl group, a n-propyl group, an isopropylgroup, a n-butyl group, and a tert-butyl group.

An example of the alkoxy group represented by any one of R₂₀₁ to R₂₀₆ isa methoxy group.

Examples of the aryl group represented by any one of R₂₀₁ to R₂₀₆include a phenyl group, a biphenyl group, a terphenyl group, a naphthylgroup, an anthracenyl group, a fluorenyl group, a phenanthryl group, abenzophenanthryl group, a chrysenyl group, and a fluoranthenyl group.

In addition, the aryl group may further have a fluorine atom, an alkylgroup such as a methyl group, an ethyl group, an isopropyl group, or atert-butyl group, an alkoxy group such as a methoxy group, or an aminogroup.

In the compound represented by the general formula [7], a carbon atombonded to a nitrogen atom of its viologen skeleton is substituted withany one of a fluorine group, an alkyl group, an alkoxy group, and anaryl group as substituents each having high hydrophobicity. Suchsubstitution is preferred because a substitution position that is liableto be oxidized is capped and hence the oxidation of the compound can besuppressed. This is because nitrogen of a tertiary amine has a highelectron-donating property and the reactivity of an sp² carbon atom thathas additionally received the effect improves.

In addition, out of the compounds each represented by the generalformula [7], a compound represented by the following general formula [8]is preferred.

In the general formula [8], all of R₂₀₃ to R₂₀₆ represent aryl groups,and R₂₁₁ to R₂₂₀ each represent a hydrogen atom or a substituentselected from the group consisting of a fluorine atom, an alkyl group,an alkoxy group, and an aryl group.

It is to be noted that the aryl group may further have a fluorine atom,an alkyl group such as a methyl group, an ethyl group, an isopropylgroup, or a tert-butyl group, an alkoxy group such as a methoxy group,or an amino group.

When all of R₂₀₃ to R₂₀₆ represent aryl groups as represented by thegeneral formula [8], R₂₀₁ and R₂₀₂ in the general formula [7] eachpreferably represent a phenyl group. This is because of the followingreason: when all of R₂₀₃ to R₂₀₆ represent aryl groups, the molecularweight of the compound increases and the compound becomes stericallybulky, and hence R₂₀₁ and R₂₀₂ in the general formula [7] eachpreferably represent a phenyl group, which is smallest among the arylgroups, from the viewpoints of sublimation purification and stericbulkiness.

[Specific Examples of Electron Acceptor-Property Compound]

Specific examples of the electron acceptor-property compound to be usedas a constituent material for the organic light emitting element of thepresent invention are shown below. However, the present invention is notlimited to these specific examples.

[Other Constituent Material for Organic Light Emitting Element]

In the organic light emitting element of the present invention, inaddition to the electron donor-property compound X and the electronacceptor-property compound Y, a known compound can be used as aconstituent material to be incorporated into the element. Examples ofsuch compound are given below.

A material having a high hole mobility is preferred as a holeinjectable/transportable material so that the injection of a hole fromthe anode may be facilitated and the injected hole can be transported tothe emission layer. In addition, a material having a high glasstransition temperature is preferred in order that the degradation offilm quality such as crystallization in the organic light emittingelement may be prevented. A triarylamine derivative, an arylcarbazolederivative, a phenylenediamine derivative, a stilbene derivative, aphthalocyanine derivative, a porphyrin derivative, poly(vinylcarbazole), poly(thiophene), and any other conductive polymer are givenas a low-molecular material or high-molecular material having holeinjection/transport performance. Further, the holeinjectable/transportable material is also suitably used for an electronblocking layer.

Specific examples of the compound to be used as the holeinjectable/transportable material are shown below. However, the compoundis of course not limited to the following.

As a light emitting material mainly involved in light emitting functionamong constituent materials for the emission layer, there are given, forexample, condensed ring compounds (such as a fluorene derivative, anaphthalene derivative, a pyrene derivative, a perylene derivative, atetracene derivative, an anthracene derivative, and rubrene), aquinacridone derivative, a coumarin derivative, a stilbene derivative,an organic aluminum complex such as tris(8-quinolinolato)aluminum, aniridium complex, a platinum complex, a rhenium complex, a coppercomplex, a europium complex, a ruthenium complex, and polymerderivatives such as a poly(phenylene vinylene) derivative, apoly(fluorene) derivative, and a poly(phenylene) derivative.

Specific examples of the compound to be used as the light emittingmaterial are shown below. However, the compound is of course not limitedto the following.

As a host or an assist material (emission assist material) to beincorporated into the emission layer, there are given, for example, anaromatic hydrocarbon compound and a derivative thereof as well as acarbazole derivative, a dibenzofuran derivative, a dibenzothiophenederivative, an organic aluminum complex such as atris(8-quinolinolato)aluminum, and an organic beryllium complex.

Specific examples of the compound to be used as the host (emission layerhost) or emission assist material to be incorporated into the emissionlayer are shown below. However, the compound is of course not limited tothe following.

An electron transportable material can be arbitrarily selected frommaterials that can transport an electron injected from the cathode tothe emission layer, and the material is appropriately selected inconsideration of, for example, the balance with the hole mobility of thehole transportable material. Examples of the material having electrontransport performance include an oxadiazole derivative, an oxazolederivative, a pyrazine derivative, a triazole derivative, a triazinederivative, a quinoline derivative, a quinoxaline derivative, aphenanthroline derivative, an organic aluminum complex, and condensedring compounds (such as a fluorene derivative, a naphthalene derivative,a chrysene derivative, and an anthracene derivative). Further, theelectron transportable material is also suitably used for the holeblocking layer.

Specific examples of the compound to be used as the electrontransportable material are shown below. However, the compound is ofcourse not limited to the following.

An electron injectable material can be arbitrarily selected frommaterials that can facilitate the injection of an electron from thecathode, and the material is selected in consideration of, for example,balance with a hole injection property. The electron injectable materialincludes the electron donor-property compound (viologen compound) thathas already been described, an n-type dopant, and a reducing dopant aswell. In addition to the viologen compound, examples of such materialhaving electron injection performance include an alkali metal, analkaline earth metal, a rare earth metal, an oxide of an alkali metal, ahalide of an alkali metal, a carbonate of an alkali metal, an alkalimetal complex, an oxide of an alkaline earth metal, a halide of analkaline earth metal, an alkaline earth metal complex, an oxide of arare earth metal, a halide of a rare earth metal, and a rare earth metalcomplex.

A constituent material for the anode desirably has as large a workfunction as possible. Examples thereof may include: metal simplesubstances such as gold, platinum, silver, copper, nickel, palladium,cobalt, selenium, vanadium, and tungsten or alloys obtained by combiningthese metal simple substances; metal oxides such as tin oxide, zincoxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide; andconductive polymers such as polyaniline, polypyrrole, and polythiophene.

One kind of those electrode substances may be used alone, or two or morekinds thereof may be used in combination. In addition, the anode may beof a single-layer construction or may be of a multilayer construction.

On the other hand, a constituent material for the cathode is desirablyone having as small a work function as possible, but is not limitedthereto. Examples thereof include: alkali metals such as lithium;alkaline earth metals such as calcium; and metal simple substances suchas aluminum, titanium, manganese, silver, lead, chromium, and gold.Alternatively, alloys obtained by combining those metal simplesubstances can be used. For example, a magnesium-silver alloy, analuminum-lithium alloy, or an aluminum-magnesium alloy can be used. Ametal oxide such as indium tin oxide (ITO) can also be utilized. Onekind of those electrode substances may be used alone, or two or morekinds thereof may be used in combination. In addition, the cathode maybe of a single-layer construction or may be of a multilayerconstruction.

In the organic light emitting element of the present invention, a lightextraction construction may be a bottom emission construction(construction in which light is extracted from a substrate side) or maybe a top emission construction (construction in which light is extractedfrom a side opposite to the substrate). In the case of the bottomemission construction, while a first electrode to be formed on thesubstrate side is a light transmissive electrode or lightsemi-transmissive electrode, a second electrode to be formed on the sideopposite to the substrate is a light reflective electrode. In addition,in the case of the top emission construction, while the first electrodeis the light reflective electrode, the second electrode is the lighttransmissive electrode or light semi-transmissive electrode. A metalconductive layer having a large thickness (of 80 nm or more and 600 nmor less) can be used as the light reflective electrode. In addition, ametal conductive layer having a small thickness (of from 15 nm to 35 nm)can be used as the light semi-transmissive electrode.

The organic light emitting element of the present invention ispreferably sealed in order that the contact of oxygen, moisture, or thelike may be suppressed. A method of sealing the organic light emittingelement of the present invention is, for example, a method involvingforming a sealing layer on the organic light emitting element. Examplesof a constituent material for the sealing layer for sealing the organiclight emitting element include materials such as: inorganic oxides,inorganic nitrides, and inorganic oxynitrides such as SiO₂, SiN, andSiON; polymer compounds such as a fluorine resin, polyparaxylene,polyethylene, a silicone resin, and a polystyrene resin; andphotocurable resins. In addition, a member formed by an atomic layerdeposition (ALD) method on the second electrode can be used as thesealing layer.

In addition, an organic film layer such as an optical interference layercan be formed on the second electrode.

The organic compound layer (such as the hole injection layer, the holetransport layer, the electron blocking layer, the emission layer, thehole blocking layer, the electron transport layer, or the electroninjection layer) for forming the organic light emitting element of thepresent invention is formed by the following method.

A dry process such as a vacuum vapor deposition method, an ionized vapordeposition method, sputtering, or a plasma process can be used for theformation of the organic compound layer for forming the organic lightemitting element of the present invention. In addition, a wet processinvolving dissolving the constituent materials in an appropriate solventand forming a layer by a known application method (such as spin coating,dipping, a casting method, an LB method, or an ink jet method) can beused instead of the dry process.

Here, when the layer is formed by the vacuum vapor deposition method,the solution application method, or the like, the layer hardly undergoescrystallization or the like and is excellent in stability over time. Inaddition, when the layer is formed by the application method, the filmcan be formed by using the constituent materials in combination with anappropriate binder resin.

Examples of the binder resin include, but not limited to, a polyvinylcarbazole resin, a polycarbonate resin, a polyester resin, an ABS resin,an acrylic resin, a polyimide resin, a phenol resin, an epoxy resin, asilicone resin, and a urea resin.

In addition, one kind of those binder resins may be used alone as ahomopolymer or a copolymer, or two or more kinds thereof may be used asa mixture. Further, a known additive such as a plasticizer, anantioxidant, or a UV absorber may be used in combination as required.

[Application of Organic Light Emitting Element]

The organic light emitting element of the present invention can be usedas a constituent member for a display apparatus or lighting apparatus.In addition, the element finds use in applications such as an exposurelight source for an image forming apparatus of an electrophotographicsystem, a backlight for a liquid crystal display apparatus, and a lightemitting apparatus including a white light source and a color filter.Examples of the color filter include filters that transmit light beamshaving three colors, i.e., red, green, and blue colors.

A display apparatus of the present invention includes the organic lightemitting element of the present invention in its display portion. It isto be noted that the display portion includes a plurality of pixels.

In addition, the pixels each include the organic light emitting elementof the present invention and a transistor as an example of an activeelement (switching element) or amplifying element configured to controlemission luminance, and the anode or cathode of the organic lightemitting element and the drain electrode or source electrode of thetransistor are electrically connected to each other. Here, the displayapparatus can be used as an image display apparatus for a PC or thelike. The transistor is, for example, a TFT element and the TFT elementis provided on, for example, the insulating surface of a substrate.

The display apparatus may be an image information processing apparatusthat includes an image input portion configured to input imageinformation from, for example, an area CCD, a linear CCD, or a memorycard, and displays an input image on its display portion.

In addition, the display portion of an imaging apparatus or inkjetprinter may have a touch panel function. The drive system of the touchpanel function is not particularly limited.

In addition, the display apparatus may be used in the display portion ofa multifunction printer.

A lighting apparatus is an apparatus configured to light, for example,the inside of a room. The lighting apparatus may emit light having anyone of the following colors: a white color (having a color temperatureof 4,200 K), a daylight color (having a color temperature of 5,000 K),and colors ranging from blue to red colors.

A lighting apparatus of the present invention includes the organic lightemitting element of the present invention and an AC/DC converter circuit(circuit configured to convert an AC voltage into a DC voltage)connected to the organic light emitting element and configured to supplya driving voltage to the organic light emitting element. It is to benoted that the lighting apparatus may further include a color filter.

An image forming apparatus of the present invention is an image formingapparatus including: a photosensitive member; a charging unit configuredto charge the surface of the photosensitive member; an exposing unitconfigured to expose the photosensitive member to form an electrostaticlatent image; and a developing device configured to develop theelectrostatic latent image formed on the surface of the photosensitivemember. Here, the exposing unit to be provided in the image formingapparatus includes the organic light emitting element of the presentinvention.

In addition, the organic light emitting element of the present inventioncan be used as a constituent member for an exposing apparatus configuredto expose a photosensitive member. An exposing apparatus including aplurality of the organic light emitting elements of the presentinvention is, for example, an exposing apparatus in which the organiclight emitting elements of the present invention are placed to form aline along a predetermined direction.

Next, the display apparatus of the present invention is described withreference to the drawings. FIG. 1 is a schematic sectional viewillustrating an example of a display apparatus including an organiclight emitting element and a TFT element connected to the organic lightemitting element. It is to be noted that the organic light emittingelement of the present invention is used as the organic light emittingelement constituting a display apparatus 1 of FIG. 1.

The display apparatus 1 of FIG. 1 includes a substrate 11 made of glassor the like and a moisture-proof film 12 for protecting a TFT element ororganic compound layer, the film being formed on the substrate. Inaddition, a metal gate electrode 13 is represented by reference numeral13, a gate insulating film 14 is represented by reference numeral 14,and a semiconductor layer is represented by reference numeral 15.

A TFT element 18 includes the semiconductor layer 15, a drain electrode16, and a source electrode 17. An insulating film 19 is formed on theTFT element 18. An anode 21 constituting the organic light emittingelement and the source electrode 17 are connected to each other througha contact hole 20.

It is to be noted that a system for the electrical connection betweenthe electrode (anode or cathode) in the organic light emitting elementand the electrode (source electrode or drain electrode) in the TFT isnot limited to the aspect illustrated in FIG. 1. In other words, one ofthe anode and the cathode, and one of the source electrode and drainelectrode of the TFT element only need to be electrically connected toeach other.

Although a plurality of organic compound layers are illustrated like onelayer in the display apparatus 1 of FIG. 1, an organic compound layer 22may be a plurality of layers. A first protective layer 24 and secondprotective layer 25 for suppressing the degradation of the organic lightemitting element are formed on a cathode 23.

When the display apparatus 1 of FIG. 1 is a display apparatus that emitswhite light, an emission layer in the organic compound layer 22 in FIG.1 may be a layer obtained by mixing a red light emitting material, agreen light emitting material, and a blue light emitting material. Inaddition, the layer may be a stacked emission layer obtained by stackinga layer formed of the red light emitting material, a layer formed of thegreen light emitting material, and a layer formed of the blue lightemitting material. Further, alternatively, the following aspect ispermitted: the layer formed of the red light emitting material, thelayer formed of the green light emitting material, and the layer formedof the blue light emitting material are, for example, arranged side byside to form domains in one emission layer.

Although the transistor is used as the switching element in the displayapparatus 1 of FIG. 1, an MIM element may be used instead of thetransistor as the switching element.

In addition, the transistor to be used in the display apparatus 1 ofFIG. 1 is not limited to a transistor using a monocrystalline siliconwafer and may be a thin-film transistor including an active layer on theinsulating surface of a substrate. In addition, a thin-film transistorusing monocrystalline silicon as the active layer, a thin-filmtransistor using non-monocrystalline silicon such as amorphous siliconor microcrystalline silicon as the active layer, a thin-film transistorusing a non-monocrystalline oxide semiconductor such as indium zincoxide or indium gallium zinc oxide as the active layer, an organictransistor using a film formed of an organic material as the activelayer, or the like can also be used. It is to be noted that thethin-film transistor is also called a TFT element.

The channel portion of the switching element (active element) accordingto this embodiment may contain an oxide semiconductor. In the switchingelement, the oxide semiconductor in the channel portion may be in anamorphous state or may be in a crystalline state. Alternatively, thesemiconductor may be in such a state that both the states (the amorphousand crystalline states) are mixed. Here, when the oxide semiconductor inthe channel portion is in a crystalline state, a specific aspect of thecrystal is, for example, a single crystal, a microcrystal, or a crystalwhose specific axis such as a C-axis is oriented. However, the specificaspect of the crystal is not limited to one kind of the aspects, and anaspect obtained by combining at least a plurality (e.g., two kinds) ofthe aspects is also naturally included. The organic light emittingelement including such switching element may be used in an image displayapparatus in which each organic light emitting element is provided as apixel, or may be used as a lighting apparatus or as an exposure portionfor exposing a photosensitive member of an image forming apparatus of anelectrophotographic system such as a laser beam printer or a copyingmachine.

The transistor in the display apparatus 1 of FIG. 1 may be formed in asubstrate such as a Si substrate. Here, the phrase “formed in asubstrate” means that the transistor is produced by processing thesubstrate itself such as a Si substrate. In other words, the presence ofthe transistor in the substrate can be regarded as follows: thesubstrate and the transistor are integrally formed.

Whether the transistor is provided in the substrate is selecteddepending on definition. In the case of, for example, a definition ofabout a QVGA per inch, the organic light emitting element is preferablyprovided in the Si substrate.

As described above, the driving of the display apparatus using theorganic light emitting element of the present invention enables displaythat has good image quality and is stable over a long time period.

Next, other applications of the organic light emitting element of thepresent invention are described. FIG. 2 is a schematic view illustratingan example of an image forming apparatus including the organic lightemitting element according to the present invention. An image formingapparatus 26 of FIG. 2 includes a photosensitive member 27, an exposurelight source 28, a developing device 30, a charging portion 31, atransferring device 32, a conveying roller 33, and a fixing device 35.

In the image forming apparatus 26 of FIG. 2, light 29 is applied fromthe exposure light source 28 to the photosensitive member 27, whereby anelectrostatic latent image is formed on the surface of thephotosensitive member 27. In the image forming apparatus 26 of FIG. 2,the exposure light source 28 includes the organic light emitting elementaccording to the present invention. In addition, in the image formingapparatus 26 of FIG. 2, the developing device 30 as a developing portionhas a developer such as toner and is configured to apply the developerto the photosensitive member 27. In the image forming apparatus 26 ofFIG. 2, the charging portion 31 is provided for charging thephotosensitive member 27. In the image forming apparatus 26 of FIG. 2,the transferring device 32 is provided for transferring a developedimage onto a recording medium 34 such as paper. It is to be noted thatthe recording medium 34 is conveyed by the conveying roller 33 to thetransferring device 32. In the image forming apparatus 26 of FIG. 2, thefixing device 35 is provided for fixing the image formed on therecording medium 34.

FIG. 3A and FIG. 3B are each a schematic plan view illustrating aspecific example of the exposure light source constituting the imageforming apparatus 26 of FIG. 2, and FIG. 3C is a schematic viewillustrating a specific example of the photosensitive memberconstituting the image forming apparatus 26 of FIG. 2. It is to be notedthat FIG. 3A and FIG. 3B have the following feature in common: aplurality of emission portions 36 (emission points) each including theorganic light emitting element are placed on an elongated substrate 28 aof the exposure light source 28. In addition, an arrow represented byreference numeral 37 represents a column direction in which the emissionportions 36 are arranged. The column direction is the same as thedirection of the axis about which the photosensitive member 27 rotates.

By the way, FIG. 3A illustrates a form in which the plurality ofemission portions 36 of the exposure light source 28 are placed alongthe long axis direction of the photosensitive member 27. On the otherhand, FIG. 3B illustrates a form in which the emission portions 36 arealternately placed in the column direction in a first column α and asecond column β. In FIG. 3B, the first column α and the second column βare placed at different positions in a row direction.

In addition, in FIG. 3B, while a plurality of emission portions 36α areplaced at a certain interval in the first column α, the second column βhas an emission portion 36β at a position corresponding to an intervalbetween the emission portions 36α in the first column α. That is, in theexposure light source of FIG. 3B, the plurality of emission portions areplaced at a certain interval in the row direction as well.

It is to be noted that the following rewording is permitted: theexposure light source of FIG. 3B is in a state where the emissionportions (36α and 36β) constituting the exposure light source are placedin, for example, a lattice, hound's-tooth, or checkered pattern.

FIG. 4 is a schematic view illustrating an example of a lightingapparatus including the organic light emitting element according to thepresent invention. The lighting apparatus of FIG. 4 includes an organiclight emitting element 38 provided on a substrate (not shown) and anAC/DC converter circuit 39. In addition, the lighting apparatus of FIG.4 may include a heat sink (not shown) corresponding to a heatdischarging portion for discharging heat in the apparatus to the outsideon, for example, a substrate surface on a side opposite to the side onwhich the organic light emitting element 38 is mounted.

EXAMPLES

Hereinafter, the present invention is described by way of Examples.However, the present invention is not limited to Examples describedbelow.

[Electron Donor-Property Compound X (Viologen Compound)]

The viologen compound as the electron donor-property compound X used inthe production of the organic light emitting element of the presentinvention was synthesized by an existing method. Specifically, asrepresented by the following reaction formula, the viologen compound wasobtained by reducing a halide salt as a precursor of the compound.

Available as a method of reducing the halide salt is, for example, (i) areduction method involving using zinc or (ii) a reduction methodinvolving using a hyposulfite ion. Here, the methods (i) and (ii) aredescribed by taking the synthesis of Exemplified Compound C1 as aspecific example. It is to be noted that the synthesis scheme ofExemplified Compound C1 is as shown below.

<Reduction Method Involving Using Zinc (Method (i))>

Compound C1-pre, zinc powder, and ethanol were loaded into a reactionvessel, and then the reaction solution was heated to reflux for 8 hours.Thus, Exemplified Compound C1 was obtained.

<Reduction Method Involving Using Hyposulfite Ion (Method (ii))>

Compound C1-pre, 10% ammonia water, sodium hyposulfite, and ethanol wereloaded into a reaction vessel, and then the reaction solution wasstirred at room temperature for 1 hour. Thus, Exemplified Compound C1was obtained.

[CV Measurement]

A halide salt as a precursor of the electron donor-property compound Xand the electron acceptor-property compound Y were subjected to CVmeasurement. Specific measurement conditions are listed below.

Measurement environment (gas atmosphere): nitrogen atmosphere

Electrolytic solution: 0.1 M tetrabutylammonium perchlorate solution inDMF

Reference electrode: Ag/Ag⁺

Counter electrode: Pt

Working electrode: glassy carbon

Measurement apparatus: electrochemical analyzer (manufactured by ALS,model 660C)

Sweeping rate: 1.0 V/s

Table 2 shows the first reduction potential value (V_(red)) of theelectron acceptor-property compound Y and the first oxidation potentialvalue (V_(ox)) of the electron donor-property compound X obtained underthe measurement conditions. It is to be noted that in each of theV_(red) and the V_(ox), in consideration of a measurement error, whenthe second decimal place of a measured value was 0, 1, 2, 8, or 9, thesecond decimal place was set to 0, and when the second decimal place ofthe measured value was 3, 4, 5, 6, or 7, the second decimal place wasset to 5.

Example 1

In this example (Example 1), an organic light emitting element of abottom emission construction in which an anode, a hole transport layer,an electron blocking layer, an emission layer, an electron transportlayer, an electron injection layer, and a cathode were formed in thestated order on a substrate was produced by a method to be describedbelow.

Indium tin oxide (ITO) was formed into a film on a glass substrate by asputtering method. Thus, the anode was formed. At this time, thethickness of the anode was set to 120 nm. Next, the substrate havingformed thereon the anode was sequentially subjected to ultrasonicwashing with acetone and isopropyl alcohol (IPA), and was then subjectedto boil washing with IPA, followed by drying. Further, the dried productwas subjected to UV/ozone washing. The substrate treated by theforegoing method was used as a transparent conductive supportingsubstrate (ITO substrate) in the next step.

Next, layers and an electrode layer shown in Table 1 below werecontinuously formed on the ITO substrate by vacuum deposition based onresistance heating in a vacuum chamber at 10⁻⁵ Pa. At this time, thelayers were formed so that an opposing electrode area became 3 mm2.

TABLE 1 Thickness Constituent material [nm] Hole transport HT2 50 layerElectron HT7 10 blocking layer Emission layer Host: EM12 30 Guest: RD1(Host:guest = 99.5:0.5 (weight ratio)) Electron ET6 50 transport layerElectron C1 (Electron donor-property 15 injection layer compound), E10(Electron acceptor-property compound) (C1:E10 = 40:60 (weight ratio))Metal electrode Al 100 layer (cathode)

The resultant organic light emitting element was driven so that itsluminance became 100 cd/m². As a result, its emission efficiency was 1.3cd/A and red light emission was observed.

Examples 2 to 7

Organic light emitting elements were each produced by the same method asthat of Example 1 with the exception that in Example 1, the constituentmaterials for the electron injection layer were changed as shown inTable 2 below. The resultant organic light emitting elements wereevaluated for their element characteristics by the same method as thatof Example 1. Table 2 shows the results.

Comparative Example 1

An organic light emitting element was produced by the same method asthat of Example 1 with the exception that in Example 1, Compound a-1shown below was used as an electron donor-property compound instead ofExemplified Compound C1. The resultant organic light emitting elementwas evaluated for its element characteristic by the same method as thatof Example 1. Table 2 shows the result.

TABLE 2 Electron injection layer V_(ox) − Donor Acceptor V_(red)Efficiency V_(ox) (V) V_(red) (V) (V) (cd/A) Example 1 C1 −1.10 E10−0.90 −0.20 1.3 Example 2 C1 −1.10 E7 −1.20 0.10 0.9 Example 3 C3 −1.20E10 −0.90 −0.30 1.4 Example 4 C3 −1.20 E7 −1.20 0 1.0 Example 5 C8 −0.90E5 −0.90 0 0.9 Example 6 B5 −1.20 E10 −0.90 −0.30 1.2 Example 7 B5 −1.20E7 −1.20 0 0.8 Comparative a-1 0.30 a-2 −0.90 1.20 No light Example 1(E10) emission

Examples 8 to 11

Organic light emitting elements were each produced by the same method asthat of Example 1 with the exception that in Example 1, the constituentmaterials for the emission layer were changed as shown in Table 3 below.The resultant organic light emitting elements were evaluated for theirelement characteristics by the same method as that of Example 1. Table 3shows the results.

TABLE 3 Emission layer Weight Dop- Weight Efficiency Luminescent Hostratio ant ratio (cd/A) color Example 8 EM3 95% BD6 5% 0.3 Blue lightemission Example 9 EM2 98% GD4 2% 1.8 Green light emission Example EM1096% RD3 4% 2.8 Red light 10 emission Example EM7 90% GD6 10% 3.7 Greenlight 11 emission

Examples 12 to 15

Organic light emitting elements were each produced by the same method asthat of Example 1 with the exception that in Example 1, the constituentmaterials for the electron injection layer were changed as shown inTable 4 below. The resultant organic light emitting elements wereevaluated for their element characteristics by the same method as thatof Example 1. Table 4 shows the results.

TABLE 4 Electron injection layer V_(ox) − Donor Acceptor V_(red)Efficiency V_(ox) (V) V_(red) (V) (V) (cd/A) Example 12 C9 −1.00 E8−1.95 0.95 1.1 Example 13 C9 −1.00 E20 −1.80 0.80 1.6 Example 14 D6−0.90 E19 −1.85 0.95 1.5 Example 15 D6 −0.90 E20 −1.80 0.90 1.4

Example 16

An organic light emitting element of a bottom emission construction asdescribed below in which an anode, a hole transport layer, an electronblocking layer, an emission layer, a hole blocking layer, an electroninjection/transport layer, and a cathode were formed in the stated orderon a substrate was produced. It is to be noted that the electroninjection/transport layer constituting the organic light emittingelement of this example is a layer that brings together the functions ofan electron injection layer and an electron transport layer.

Layers and an electrode layer shown in Table 5 below were continuouslyformed on the ITO substrate produced in Example 1 by vacuum depositionbased on resistance heating in a vacuum chamber at 10⁻⁵ Pa. At thistime, the layers were formed so that an opposing electrode area became 3mm².

TABLE 5 Thickness Constituent material [nm] Hole transport layer HT2 50Electron blocking layer HT7 10 Emission layer Host: EM14 20 Guest: RD1(Host:guest = 99.5:0.5 (volume ratio)) Hole blocking layer EM15 10Electron E19, C1 53 injection/transport layer ^((Note 1)) Metalelectrode layer Aluminum 120 (Cathode) ^((Note 1)) The electroninjection/transport layer is a stack in which E19 (50 nm, acceptorlayer) and C1 (3 nm, donor layer) are stacked in the stated order.

The resultant organic light emitting element was driven so that itsluminance became 100 cd/m². As a result, its emission efficiency was 3.6cd/A and red light emission was observed.

Examples 17 to 19 and Comparative Example 2

Organic light emitting elements were each produced by the same method asthat of Example 16 with the exception that in Example 16, theconstituent materials for the electron injection/transport layer werechanged as shown in Table 6 below. The resultant organic light emittingelements were evaluated for their element characteristics by the samemethod as that of Example 16. Table 6 shows the results.

TABLE 6 Electron injection/transport layer Acceptor layer Donor layerV_(ox) − V_(red) Efficiency V_(red) (V) V_(ox) (V) (V) (cd/A) Example 16E19 −1.85 C1 −1.10 0.75 3.6 Example 17 E20 −1.80 C1 −1.10 0.70 3.5Example 18 E19 −1.85 C9 −0.90 0.95 1.9 Example 19 E20 −1.80 C9 −0.900.90 2.0 Comparative E5 −2.30 No light Example 2 emission

Example 20

In this example, an organic light emitting element was produced by thesame method as that of Example 16 with the exception that in Example 16,the constituent material for the metal electrode layer (cathode) waschanged to silver.

The resultant organic light emitting element was driven so that itsluminance became 100 cd/m². As a result, its emission efficiency was 4.2cd/A and red light emission was observed.

Examples 21 to 23

Organic light emitting elements were each produced by the same method asthat of Example 20 with the exception that in Example 20, theconstituent materials for the electron injection/transport layer werechanged as shown in Table 7 below. The resultant organic light emittingelements were evaluated for their element characteristics by the samemethod as that of Example 20. Table 7 shows the results.

TABLE 7 Electron injection (and electron transport) layer Acceptor layerDonor layer V_(ox) − V_(red) Efficiency V_(red) (V) V_(ox) (V) (V)(cd/A) Example 20 E19 −1.85 C1 −1.10 0.75 4.2 Example 21 E20 −1.80 C1−1.10 0.70 4.1 Example 22 E19 −1.85 C9 −0.90 0.95 2.5 Example 23 E20−1.80 C9 −0.90 0.90 2.7 Comparative E5 −2.30 No light Example 3 emission

Example 24

In this example, an organic light emitting element of a top emissionconstruction in which a first electrode (anode), a hole transport layer,an electron blocking layer, an emission layer, a hole blocking layer, anelectron injection/transport layer, and a second electrode (cathode)were formed in the stated order on a substrate was produced by a methodto be described below.

An aluminum metal and indium tin oxide (ITO) were formed into films andstacked in the stated order on a glass substrate (substrate) by asputtering method. Thus, the first electrode as an anode was formed. Atthis time, the thickness of the aluminum film constituting the firstelectrode was set to 100 nm and the thickness of the ITO filmconstituting the first electrode was set to 30 nm. Next, the substratehaving formed thereon the first electrode was sequentially subjected toultrasonic washing with acetone and isopropyl alcohol (IPA), and wasthen subjected to boil washing with IPA, followed by drying. Further,the dried product was subjected to UV/ozone washing, to thereby obtainan ITO substrate.

Next, layers and the second electrode as a cathode shown in Table 8below were continuously formed on the ITO substrate by vacuum depositionbased on resistance heating in a vacuum chamber at 10⁻⁵ Pa. At thistime, the layers were formed so that an emission area in which the firstelectrode and the second electrode overlapped each other became 4 mm².

TABLE 8 Thickness Constituent material [nm] Hole transport layer HT2 200Electron blocking HT7 10 layer Emission layer Host: EM14 20 Guest: RD1(Host:guest = 99.5:0.5 (volume ratio)) Hole blocking layer EM15 10Electron E19, C1 33 injection/transport layer ^((Note 1)) Secondelectrode Aluminum, silver 30 (cathode) ^((Note 2)) ^((Note 1)) Theelectron injection/transport layer is a stack in which E19 (30 nm,acceptor layer) and C1 (3 nm, donor layer) are stacked in the statedorder. In addition, V_(ox)− V_(red) in Example 24 is 0.75 V. ^((Note 2))The second electrode is a stack in which aluminum (5 nm) and silver (25nm) are stacked in the stated order.

It is to be noted that in the organic light emitting element produced inthis example, the second electrode was a light semi-transmissiveelectrode, and was a stacked electrode formed of aluminum (5 nm) andsilver (25 nm) in consideration of a reflectance, absorption, and aconductivity. In addition, a cavity construction in which lightextraction efficiency was improved by utilizing optical interference wasadopted, and the thicknesses of the respective layers were determined sothat their interference conditions coincided with each other.

The resultant organic light emitting element was driven so that itsluminance became 100 cd/m². As a result, its emission efficiency was 3.7cd/A and red light emission was observed.

[Results and Discussion]

As described in Examples, when the electron injection layer is a mixedfilm containing the viologen compound X represented by the generalformula [1] as an electron donor-property compound and the electronacceptor-property compound Y, an electron can be injected from theelectrode (cathode) and hence light emission from the emission layer canbe obtained.

As described above, the electron injection layer of the organic lightemitting element of the present invention contains the electrondonor-property viologen compound X (viologen compound represented by thegeneral formula [1]) and the electron acceptor-property compound Y.Accordingly, the organic light emitting element of the present inventionis an element stable against the air.

According to the present invention, the organic light emitting elementhaving stable performance in the air can be provided.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-060339, filed Mar. 24, 2014 and Japanese Patent Application No.2015-001212, filed Jan. 7, 2015, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. An organic light emitting element, comprising: ananode; a cathode; and an emission layer placed between the anode and thecathode, wherein: the organic light emitting element further comprises afirst organic compound layer placed between the cathode and the emissionlayer, and a second organic compound layer placed between the emissionlayer and the first organic compound layer, and contacted with the firstorganic compound layer; the first organic compound layer contains afirst organic compound; the second organic compound layer contains asecond organic compound; and the first organic compound comprises aviologen compound represented by the following general formula [1] andthe second organic compound comprises an organic compound different fromthe viologen compound:

in the formula [1], R₁ to R₆ each represent a hydrogen atom or asubstituent selected from the group consisting of a fluorine atom, analkyl group, an alkoxy group, an aryl group, and a heteroaryl group,when any one of R₁ to R₆ represents an alkyl group or an alkoxy group,the alkyl group or the alkoxy group may further have a fluorine atom,and when any one of R₁ to R₆ represents an aryl group or a heteroarylgroup, the aryl group or the heteroaryl group may further have afluorine atom, an alkyl group, an alkoxy group, or an amino group. 2.The organic light emitting element according to claim 1, wherein thefirst organic compound layer is contacted with the cathode.
 3. Anorganic light emitting element, comprising: an anode; a cathode; and anemission layer placed between the anode and the cathode, wherein: theorganic light emitting element further comprises an organic compoundlayer placed between the cathode and the emission layer; the organiccompound layer contains a first organic compound and a second organiccompound; and the first organic compound comprises a viologen compoundrepresented by the following general formula [1] and the second organiccompound comprises an organic compound different from the viologencompound:

in the formula [1], R₁ to R₆ each represent a hydrogen atom or asubstituent selected from the group consisting of a fluorine atom, analkyl group, an alkoxy group, an aryl group, and a heteroaryl group,when any one of R₁ to R₆ represents an alkyl group or an alkoxy group,the alkyl group or the alkoxy group may further have a fluorine atom,and when any one of R₁ to R₆ represents an aryl group or a heteroarylgroup, the aryl group or the heteroaryl group may further have afluorine atom, an alkyl group, an alkoxy group, or an amino group. 4.The organic light emitting element according to claim 3, wherein acontent of the second organic compound is more than 0 wt % and 80 wt %or less with respect to a total of the viologen compound and the secondorganic compound.
 5. The organic light emitting element according toclaim 1, wherein the viologen compound and the second organic compoundsatisfy the following formula [4]:|V _(red) −V _(ox)|≦1.0 V  [4] in the formula [4], V_(ox) represents afirst oxidation potential value of the viologen compound and V_(red)represents a first reduction potential value of the second organiccompound.
 6. The organic light emitting element according to claim 1,wherein the second organic compound is represented by any one of thefollowing general formulae [2-1] to [2-21], [3-1], and [3-2]:

in the formulae [2-1] to [2-21], [3-1], and [3-2], R₂₁ to R₉₉ and R₁₀₃to R₁₅₉ each represent a hydrogen atom or a substituent selected fromthe group consisting of an alkyl group, an alkoxy group, an aryl group,a heteroaryl group, and a fluorine atom, and when any one of R₂₁ to R₉₉and R₁₀₃ to R₁₅₉ represents an aryl group or a heteroaryl group, thearyl group or the heteroaryl group may further have an alkyl group, analkoxy group, an aryl group, a heteroaryl group, or a fluorine atom; inthe formula [3-1], a unit Q represents a basic structure represented byany one of the formulae [2-1] to [2-21] or a partial structure includingan aromatic ring having 6 to 30 carbon atoms, m represents an integer offrom 0 to 6, and a unit P represents any one of the followingsubstituents:

in the formulae, R₁₀₀ and R₁₀₁ each represent a substituent selectedfrom the group consisting of a hydrogen atom, an alkyl group, an alkoxygroup, an aryl group, a heteroaryl group, and a fluorine atom, and whenany one of R₁₀₀ and R₁₀₁ represents an aryl group or a heteroaryl group,the aryl group or the heteroaryl group may further have an alkyl group,an alkoxy group, an aryl group, a heteroaryl group, or a fluorine atom,and * represents an atomic bonding with the unit Q; and in the formula[3-2], a unit T represents a partial structure including an aromaticring having 6 to 30 carbon atoms or a partial structure including afive- or six-membered heterocyclic structure formed of a carbon atom andan oxygen atom, n represents an integer of from 0 to 6, and a unit Zrepresents any one of the following substituents:

in the formulae, R₁₀₂ represents a substituent selected from the groupconsisting of a hydrogen atom, an alkyl group, an alkoxy group, an arylgroup, a heteroaryl group, and a fluorine atom, and when R₁₀₂ representsan aryl group or a heteroaryl group, the aryl group or the heteroarylgroup may further have an alkyl group, an alkoxy group, an aryl group, aheteroaryl group, or a fluorine atom, and * represents an atomic bondingwith the unit T.
 7. The organic light emitting element according toclaim 1, wherein the viologen compound is represented by the followinggeneral formula [6]:

in the general formula [6], Ar₁ and Ar₂ each represent an aryl groupthat may have a fluorine atom, an alkyl group, an alkoxy group, or anamino group.
 8. A display apparatus, comprising a plurality of pixels,wherein at least one of the plurality of pixels includes the organiclight emitting element of claim 1, and an active element connected tothe organic light emitting element.
 9. A display apparatus, comprising aplurality of pixels, wherein at least one of the plurality of pixelsincludes the organic light emitting element of claim 3, and an activeelement connected to the organic light emitting element.
 10. The displayapparatus according to claim 8, wherein the active element comprises atransistor and the transistor has an oxide semiconductor as an activelayer.
 11. An image information processing apparatus, comprising: aninput portion configured to input image information; and a displayportion configured to display an image, wherein the display portioncomprises the display apparatus of claim
 8. 12. A lighting apparatus,comprising: the organic light emitting element of claim 1; and an AC/DCconverter configured to supply a driving voltage to the organic lightemitting element.
 13. A lighting apparatus, comprising: the organiclight emitting element of claim 3; and an AC/DC converter configured tosupply a driving voltage to the organic light emitting element.
 14. Thelighting apparatus according to claim 12, wherein: the organic lightemitting element is connected to a transistor; and the transistor has anoxide semiconductor as an active layer.
 15. An image forming apparatus,comprising: a photosensitive member; a charging portion configured tocharge the photosensitive member; an exposure portion configured toexpose the photosensitive member; and a developing portion configured toapply a developer to the photosensitive member, wherein the exposureportion includes the organic light emitting element of claim
 1. 16. Animage forming apparatus, comprising: a photosensitive member; a chargingportion configured to charge a surface of the photosensitive member; anexposure portion configured to expose the photosensitive member; and adeveloping portion configured to apply a developer to the photosensitivemember, wherein the exposure portion includes the organic light emittingelement of claim
 3. 17. The image forming apparatus according to claim15, wherein: the organic light emitting element is connected to atransistor; and the transistor has an oxide semiconductor as an activelayer.
 18. An exposing apparatus, which is configured to expose aphotosensitive member, the exposing apparatus comprising a plurality ofemission points each including the organic light emitting element ofclaim 1, wherein the plurality of emission points are placed to form aline along a long axis direction of the photosensitive member.
 19. Theexposing apparatus according to claim 18, wherein: the organic lightemitting element is connected to a transistor; and the transistor has anoxide semiconductor as an active layer.
 20. An exposing apparatus, whichis configured to expose a photosensitive member, the exposing apparatuscomprising a plurality of emission points each including the organiclight emitting element of claim 3, wherein the plurality of emissionpoints are placed to form a line along a long axis direction of thephotosensitive member.